Devices and methods for spectroscopic analysis

ABSTRACT

The present invention relates to devices and methods for spectrometric analysis of light-emitting samples. The device comprises a particle beam source, which generates a primary particle beam directed to the sample in such a way that the primary particle beam is incident on the sample and photons are released from the sample due to the interaction between primary particle beam and sample material. Moreover, the device comprises a plurality of light-pickup elements, which are suitable for capturing the photons released from the sample, wherein the light-pickup elements capture the photons emitted in the respectively assigned solid-angle range. Furthermore, the device comprises conduction elements, which are embodied to forward captured photons to an evaluation unit, and an analysis system, which comprises a plurality of evaluation units in such a way that photons captured by each light-pickup element are analyzed spectrally.

The invention relates to methods and devices for spectrometric analysisof luminescent samples.

Luminescence is understood to mean the emission of light, i.e.electromagnetic radiation with wavelengths in the visible or adjacentwavelength range (infrared and ultraviolet). In order to be able toobserve luminescence, a material having luminescent properties isexcited by excitation processes to emit light. By way of example, theexcitation can be brought about by irradiation with photons orelectrons. This is referred to as photoluminescence in the case ofexcitation by photons, e.g. via UV light. Luminescence is referred to ascathodoluminescence (CL) if the light emission was excited by theincidence of electrodes which were previously emitted by a cathode andaccelerated in an electric field. The duration of the light emission canbe very different and range between a few milliseconds and a number ofhours: quickly decaying luminescence appearances are referred to asfluorescence and long-term light emission is referred to asphosphorescence.

The generation of luminescence phenomena in semiconductors and inorganiccrystals can be explained by the energy band model from semiconductorphysics. In accordance with this model, the energy states in which theelectrons can be situated are combined to form bands, wherein adistinction is made between a valence band and a conduction band. Ifprimary particles, that is to say e.g. photons or electrons, areincident on the sample material, energy can be transferred from anincident primary particle to an electron of the sample material. If theenergy is transferred to a valence electron, this electron can be liftedinto an energy state assigned to the conduction band. However, in thecase of fluorescence, the conduction electron immediately recombineswith an electron hole in the valence band, i.e. returns to the energylevel of the valence band. In the process, energy is released, which isemitted in the form of light quanta, the energy of which corresponds tothe transition energy. In addition to such a direct band/bandtransition, indirect band transitions may also occur, in which part ofthe released energy is emitted in the form of heat (non-radiatingrecombination of the charge carriers).

In the case of organic molecules, the generation of luminescence canalso be explained by virtue of electrons, which were previously liftedby excitation processes from an energetic ground state into an excitedstate, returning to the ground state and emitting light in the process.

The emitted luminescence light can be detected and used to generateimages of the sample or to analyze the material properties of thesample. Thus, conclusions can be drawn about the properties of theluminescent material, preferably on the basis of intensity, spectralcomposition and time-dependent change in the intensity of theluminescence light. By way of example, this allows recombination centersto be determined, or lattice defects, impurities, phase formations orinhomogeneities in the dopant distribution to be identified. Typicalexamples of samples in which luminescence phenomena can be examined aresemiconductor components, ceramics (e.g. technical catalysts), inorganiccrystals and biomedical samples (e.g. tissue samples). It is alsopossible to examine organic compounds, for example in order to be ableto identify chemical defects in the polymer structure of plastics, sinceundesired breaks in the polymer chains may, at a later stage, emanatefrom such defects.

However, integrated detection of the luminescence light, i.e. thedetection of a summed signal, only supplies qualitative results sincethe cause for a change in the summed signal may lie in the simultaneouschange of a plurality of parameters. It is therefore more advantageousto detect the luminescence light in an angle-resolved, spatiallyresolved and time-resolved manner and, in the process, register therespective wavelength spectrum of the released photons. The spectralanalysis allows the electron transition responsible for the lightemission to be identified since there is a direct relationship betweentransition energy and wavelength of the emitted photons from the waveequation and Planck's constant.

Since light is emitted in all directions, the largest possible solidangle over the sample should be registered so that as many photonsemerging from the sample material as possible are detected. Theangle-resolved detection allows conclusions to be drawn about materialproperties and texture of the sample, since the assumption can be madethat photons originating from different depths of the structured sampleare emitted in different solid angles. The time-resolved detectionrenders it possible to register the kinetics of the charge carrierrecombinations, that is to say e.g. lifespan, reaction times, scatteringmechanisms or capturing times. Moreover, it is advantageous to achieve ahigh spatial resolution. By way of example, this is possible incathodoluminescence, since the incident electron beam can be focused onthe sample surface, and so it is usually possible to achieve a spatialresolution of less than one micrometer.

In order to examine the spectral composition, use is generally made ofspectrometers which typically comprise an entry slit (entry aperture), adispersion element and a detector. A prism or a grating can serve asdispersion element. If the light to be analyzed passes the dispersionelement, the spectral components of the light are deflected in differentspatial directions: a spectrum is generated, which can be imaged via thedetector and/or stored and processed for analysis purposes.Alternatively, use can also be made of filter-based spectrometers.

When the light beam passes through a diffraction grating, intensitymaxima of the zero order of diffraction and of higher orders ofdiffraction are generated. The zero-order maximum is to be understood tomean the portion of the light which passes the diffraction gratingwithout being spectrally divided. However, in conventionalspectrometers, the zero order is not evaluated but rather suppressed bylight traps in order to prevent interference of the spectrometricmeasurement.

Usually, spectrometers need to be continuously referenced duringoperation in order to compensate for changes in the surroundinginfluences—e.g. temperature variations—which would have a negativeeffect on the measurement. In order to carry out the referencing, it isconventional to interrupt the measurement at specific time intervals andto modify the measurement arrangement in such a way that a minimum value(dark reference) and a maximum value (bright reference) can be defined,between which all future measured values can then be arranged.

BRIEF DESCRIPTION OF THE RELATED PRIOR ART

DE 19731226 describes an imaging CL spectrometer for recording CL imagesand CL spectra in electro-optical instruments.

Furthermore, a combined device of light microscope and electron or ionmicroscope is known, which comprises a light-collecting device and adetector for detecting luminescence light.

Moreover, methods have been proposed in which the primary beam isemitted and directed to the sample and the luminescence light releasedfrom the sample material is captured.

Moreover, methods and devices for time-resolved spectroscopy via a PMDsensor are known, as is the use of compact miniaturized spectrometers.

The following documents can be considered to be the closest prior art:

-   -   WO2012/008836A    -   DE 102009046211    -   DE 19731226

OVERVIEW OVER THE INVENTION

It is an object of the present invention to propose devices and methodsvia which the wavelength spectrum of luminescence light can be detected.In the process, the detected photons are preferably registered in anangle-resolved manner. Alternatively, the detected photons areregistered simultaneously in a spatially resolved and angle-resolvedmanner. Moreover, methods and devices are proposed, via which photonscan be registered in a spatially resolved, angle-resolved andtime-resolved manner.

According to the invention, this object is achieved by a device forspectrometric analysis of light-emitting samples, wherein the devicecomprises: a particle beam source which generates a primary particlebeam directed to the sample so that the primary particle beam isincident on the sample and photons are released from the sample due tothe interaction between primary particle beam and sample material;light-pickup elements suitable for capturing the photons released fromthe sample, wherein each light-pickup element captures photons emittedin a solid-angle range; conduction elements embodied to forward capturedphotons to an evaluation unit; and an analysis system comprising aplurality of evaluation units in such a way that photons captured byeach light-pickup element are analyzed spectrally. The object is alsoachieved by a device for spectrometric analysis of light-emittingsamples, wherein the device comprises: an imaging grating arranged sothat photons released by the sample are dispersed; and a detector whichdetects the spectrum generated by dispersion. Advantageousconfigurations of the invention are specified by the disclosure.Moreover, the object is achieved by a method for spectroscopic analysisof samples, comprising the following steps: a) generating a primaryparticle beam directed to the sample in such a way that the primaryparticle beam is incident on the sample and photons are released fromthe sample due to the interaction between primary particle beam andsample material and released photons are able to move along amultiplicity of possible trajectories, wherein each one of the possibletrajectories n is characterized by an elevation angle hn and an azimuthangle an and equivalent or similar trajectories are combined tosolid-angle ranges of the trajectories; b) simultaneously capturing thereleased photons via a multiplicity of light-pickup elements, whereineach individual light-pickup element corresponds to a solid-angle rangeof the trajectories; c) forwarding the captured photons to an analysissystem, wherein the analysis system comprises a multiplicity ofevaluation units in such a way that an evaluation unit is assigned toeach light-pickup element, and d) recording optical spectra in such away that a spectrum is generated for each light-pickup element on thebasis of the photons captured by this light-pickup element, and byadvantageous configurations specified by the disclosure.

The particle-optical device according to the invention can be a scanningelectron microscope (SEM), an ion microscope with focused ion beam(FIB), a light microscope or a combination instrument, which comprisestwo or more of the aforementioned particle-optical devices. It is alsofeasible to use a transmission electron microscope (TEM) asparticle-optical device.

In an advantageous embodiment, the particle-optical device comprises atleast one particle beam source. The particle beam source generates aprimary particle beam of electrically charged particles, which isdirected to the sample. The sample consists of at least one chemicalsubstance with luminescence properties. The particles of the primaryparticle beam incident on the sample interact with theluminescence-capable sample material. As a result, interaction productsin the form of photons are released from the sample. Since the focus ofthe primary particle beam is generally guided sequentially over thesample surface, the luminescence light is in each case only emitted onthe impact point of the primary particle beam, and so the luminescencelight can be detected in a spatially resolved manner.

In principle, each location on the sample can emit light, and so eachlocation on the sample can be considered to be a punctiform lightsource. Proceeding from a light source, photons are potentially emittedin all directions, wherein the photons can follow a multiplicity ofpossible trajectories. In each case, these trajectories can be describedby an elevation angle h_(n) and an azimuth angle a_(n). Since there areinfinitely many possible trajectories, it is advantageous to grouptrajectories with a similar profile—that is to say trajectories that canbe described by the same, approximately the same or similar solidangles—by virtue of defining that these trajectories belong to the samesolid-angle range of the trajectories. The center points of the varioussolid-angle ranges in each case lie under different angles in relationto the incident primary particle beam, to be precise both in thedirection of the elevation angle (vertical angle) and in the directionof the azimuth (horizontal angle).

Using a device in accordance with the present invention, it is possibleto distinguish between photons moving in different solid-angle rangesand to detect these separately from one another. To this end, the devicecomprises a multiplicity of light-pickup elements, which are arrangedover the sample surface in such a way that as many solid-angle ranges aspossible can be registered and that each light-pickup element isassigned to a specific solid-angle range of the trajectories. Thelight-pickup elements are suitable for picking up and forwardingphotons. It is advantageous if each light-pickup element is connected toa conduction element. However, it is also feasible for two or morelight-pickup elements to be connected to one conduction element. Theconduction elements are suitable for forwarding the photons picked up bya light-pickup element to an evaluation unit, via which the wavelengthspectrum of the photons can be analyzed. Thus, this means that eachevaluation unit is assigned to a solid-angle range of the trajectoriesvia the direct assignment of light-pickup elements, conduction elementand evaluation unit to one another. The evaluation units can be embodiedas the channels of a multi-channel spectrometer. A multi-channelspectrometer—sometimes also referred to as a multi-beam spectrometer—isunderstood to mean a spectrometer which can record a plurality ofcomplete spectra in parallel and, for example, is embodied in the formof a multi-channel Offner spectrometer. Offner-type spectrometers havebeen known for a relatively long time and typically comprise an entryslit, two concave mirrors and a diffraction grating, lying on a convexmirror, arranged between the mirrors. However, the invention is notrestricted to an Offner spectrometer but can be carried out with anyother multi-channeled spectrometer, wherein the signal readout can besimultaneous or in a time-offset manner. Alternatively, the evaluationunits can be embodied as a multiplicity of miniaturized spectrometerssuch that a miniature spectrometer is assigned to each light-pickupelement in this case.

Both embodiment alternatives render it possible to detect photons in anangle-resolved manner and to record the wavelength spectrum of thedetected photons. For the spectral measurement, use can be made ofspectrometers which, for example, record the wavelength range from UV toNIR (185 nm-2500 nm). Under vacuum conditions, it may be advantageous towork with wavelengths under 185 nm, for example 120 nm or less, or withwavelengths over 2500 nm, for example with 10 000 nm.

By the use of time-resolving photon detectors, it is moreoveradditionally possible to detect the spectra in a time-resolved manner.

Subsequently, the obtained wavelength spectra can be calculated bymathematical algorithms on the basis of chemical statistics(chemometrics) and analyzed and evaluated with the aid of availabledatabases. The processes applied there are oriented to the demands ofthe respective application. A further advantageous embodiment comprisesa first spectrometer which uses the radiation portion undergoinghigher-order diffraction, that is to say e.g. first, second or thirdorder. Moreover, this embodiment comprises a second spectrometer whichuses the radiation portion of the zero-order diffraction. The radiationportion of the zero order usually remains unused in conventionalspectrometric measurement designs, even though this radiation portioncontains the whole spectrometric information and makes up approximately50% of the irradiated energy. By using the zero diffraction orderintensity maximum, the second spectrometer can be operated at the sametime as the first spectrometer, without a performance loss occurring inthe operation of the first spectrometer.

A further aspect of the invention comprises the simultaneous or timelyreferencing of the measured spectra. Here, the referencing preferablytakes place within a time window that is smaller than the time windowwithin which a change in the measurement design, which would requirecompensation, is expected. It is particularly advantageous if thespectroscopic measurement is not interrupted for referencing.

EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention will be explained below on thebasis of figures. Here, components which correspond to one another interms of the structure and function thereof are provided with referencesigns that have the same numerals but are complemented with anadditional letter to distinguish between these.

FIG. 1 shows a section through a model of a device according to theinvention.

FIG. 2 schematically shows a section through an advantageous embodiment.

FIG. 3 schematically shows a section through a further advantageousembodiment.

FIG. 4 schematically shows a section through advantageous embodiments ofthe light-entry openings.

FIGS. 5a and 5b schematically show a further advantageous embodiment ofthe device according to the invention. FIG. 5a shows a top view, FIG. 5bshows a sectional view.

FIG. 6 schematically shows the sectional view of a further advantageousembodiment.

FIG. 7 schematically shows a section through a further advantageousembodiment.

FIG. 8 shows a flowchart of a method according to the invention.

In FIGS. 2, 3 and 7, a sectional plane is depicted in an exemplarymanner, wherein the view in a further sectional plane (not depictedhere) perpendicular to the depicted sectional plane would be the same orsimilar.

FIG. 1 schematically shows a special exemplary embodiment. FIG. 1depicts a particle-optical device 101, which may be embodied as anelectron beam instrument, for example as a scanning electron microscope.The particle-optical device 101 comprises a particle beam source 109,which is situated in a particle-optical column 106 and generates aprimary particle beam 104, which is exposed to an acceleration voltage.The primary particle beam 104 is directed to the sample 103. The primaryparticle beam 104 is focused with the aid of lens-element systems 110,111. After passing through an aperture stop 112, the focus of theparticle beam is, via a deflection system 113, directed to the sample103 to be examined and moved over the surface of the sample 103line-by-line. The primary particle beam 104 can advantageously bemodulated, for example by virtue of being able to be switched on and offor by virtue of the mean energy of the primary particles being able tobe varied. The sample 103 consists of material with luminescentproperties and is situated on a displaceable sample stage within asample chamber 102, in which vacuum conditions are prevalent and whichis embodied for holding a sample 103. The device 101 furthermorecomprises a detection device 105, which is suitable to detect thephotons released from the sample 103. The detected photons are forwardedto an analysis system 107 and evaluated there.

In particularly advantageous embodiments, the particle-optical device101 moreover comprises at least one further detector 108, with the aidof which interaction products, which are generated by the interactionbetween primary particle beam 104 and sample material 103, can bedetected. In addition to photons, other interaction products can also begenerated, for example secondary electrons (SE) or back-scatteredelectrons (BSE). Usually, a BSE detector and/or an SE detector are usedfor detecting these interaction products, depending on whetherback-scattered electrons (BSE) and/or secondary electrons (SE) are to beused for image generation. It is also conceivable to detect furtherinteraction products using other suitable detectors, e.g. an x-raydetector.

The invention can also be carried out using a particle-optical devicewhich is embodied as ion beam instrument or two-beam microscope. Inprinciple, ion beam instruments and electron beam instruments havesimilar design. However—in contrast to electron beam instruments—ionbeam instruments have an ion source as particle beam source instead ofan electron source and only have electrostatic lens elements instead ofmagnetic lens elements or combined electrostatic/magnetic lens elements.Moreover, depending on the polarity of the ions, the polarities of thepotentials and potential differences applied to the various componentsnaturally also need to be adapted accordingly. A two-beam microscope isto be understood to mean a combination instrument made of an electronbeam instrument and an ion beam instrument. A two-beam microscopecomprises two particle beam sources which generate primary particlebeams, to be precise an electron source situated in an electron-opticalcolumn and able to generate an electron beam, and an ion source situatedin an ion-optical column and able to generate an ion beam.

FIG. 2 shows an advantageous embodiment of the device according to theinvention. The detection device 105 comprises a multiplicity oflight-pickup elements 202 and is situated within an evacuated samplechamber 209, which is delimited by a wall 208. The light-pickup elements202 are arranged over the sample 203 and are embodied as collectingoptical units. Here, a collecting optical unit can be embodied asfree-beam optical unit or as fiber-optical unit. It was found to beparticularly advantageous if the light-pickup elements 202 are arrangedin such a way that they form a hemispherical surface over the surface ofthe sample 203. Stated differently: the light-pickup elements 202 are—asdepicted in a section in FIG. 2—arranged on a segment of a sphericalsurface. It is particularly advantageous if the intermediate surfaces210 between the light-pickup elements 202, lying on the segment of thespherical surface, are configured from light-absorbing material suchthat stray-light effects are avoided. An opening situated in thecontinuation of the optical axis 104, 201 of the particle-optical device101 is preferably cut out in or near the center of the segment of thespherical surface. The primary particle beam 201 is directed to thesample surface 203 through this opening. Depending on the geometric formand/or emission property of the sample, it is also feasible for thelight-pickup elements 202 not to form a hemispherical surface but ratherto be arranged in a different shape spanning over the sample.

It was found to be advantageous if the device overall comprises two ormore light-pickup elements. It is particularly advantageous if thedevice comprises seven light-pickup elements such that seven solid-angleranges can be registered accordingly. It is also feasible for the deviceto comprise ten or more than ten, e.g. 100, light-pickup elements.However, it should be noted in the process that although, on the onehand, the solid-angle resolution is improved with increasing number oflight-pickup elements, on the other hand, the radiation portion incidenton the individual light-pickup element is reduced, and so thesensitivity of the measurement arrangement is reduced. Therefore, thenumber of light-pickup elements should be selected in such a way that,depending on the type of application, a compromise is found betweenachievable angular resolution and desired sensitivity. Photons releasedby the sample material 203 are registered by the collecting opticalunits 202. Here, each collecting optical unit 202 registers the photonsemitted in the associated solid-angle range 204. Thus, this means thateach collecting optical unit 202 captures photons moving alongtrajectories 206 corresponding to a solid-angle range 204. Each of thelight-pickup elements 202 embodied as collecting optical unit isconnected to a miniature spectrometer 205, and so the photons capturedin each case with a collecting optical unit 202 are forwarded to anassigned miniature spectrometer 205. By way of example, suchminiaturized spectrometers 205 are known from DE 10304312. The spatialrequirements of a miniature spectrometer 205 can typically be less than125 mm³. Due to the small dimensions thereof, the miniaturespectrometers 205 can be placed in the vicinity of the measurementpoint, i.e. at the location at which the primary particle beam isincident on the sample and triggers the light emission, and so these,firstly, are able to register a large solid angle and, secondly, do notshadow further detectors which detect e.g. secondary electrons orback-scattered electrons. The integration times of the miniaturespectrometers 205 are usually a few milliseconds. The miniaturespectrometers 205 can be embodied as single-channel spectrometers or asmulti-channel spectrometers, for example with two, three or morechannels.

The miniature spectrometers 205 generate spectra of the respectivelydetected luminescence light. The obtained spectra are forwarded to ananalysis system 207, stored and evaluated. In an alternativeconfiguration of this embodiment, the generated spectra are stored andevaluated in miniature spectrometers 205.

What is common to both configurations is that the obtained spectra canrespectively be assigned to a specific solid-angle range of therespective photon trajectories. Therefore, it is thus possible to detectthe luminescence light in an angle-resolved manner and to analyze itspectrally. The obtained spectra can then be calculated by mathematicalalgorithms on the basis of chemical statistics (chemometrics) and beanalyzed and evaluated with the aid of available databases.

Since the luminescence light is respectively only emitted at the pointof incidence of the primary particle beam, a spatial resolution of theluminescence signal can moreover be achieved if the focus of the primaryparticle beam is guided, perpendicular to the optical axis thereof, overthe sample surface in a time-sequential manner and the respectiveangle-resolved and spectrally resolved signal is assigned to that pointon the sample on which the primary particle beam is incident at therespective time.

In a further advantageous embodiment, which is depicted in FIG. 3, thelight-pickup elements 302 are embodied as light-entry openings ofoptical fibers 307. The optical fibers 307 can have a diameter between50 μm and 800 μm, preferably between 80 μm and 100 μm. It is alsofeasible for the optical fibers 307 to have a diameter of less than 50μm or more than 800 μm. The light-entry openings 302 are arranged on theside of the optical fibers 307 facing the sample 303. Each light-entryopening 302 collects light which was emitted in a solid-angle range 304of the trajectories 308. Photons which were picked up by the light-entryopenings 302 are forwarded via the optical fibers 307 to the entry slit305 of a multi-channel spectrometer 306. The multi-channel spectrometer306 can preferably comprise an integrated evaluation unit. By way ofexample, the multi-channel spectrometer 306 can be embodied as an Offnerspectrometer with e.g. 30 channels such that 30 spectra can be recordedsimultaneously. It was also found to be advantageous in this embodimentif the light-entry openings 302 are arranged on the surface of thespherical segment. Thus, this means that the multiplicity of light-entryopenings 302 in their totality form the shape of a segment of aspherical surface. The individual light-entry openings 302 comprisecollecting optical units or free-beam optical units. If the focus of theprimary particle beam 301—as described in relation to FIG. 2—is guidedtime sequentially over the sample surface, it is also possible to recordspectra with a spatial and/or angular resolution using this embodiment.

Furthermore, a time-resolving photon detector, e.g. a PMD chip can beused in the employed multi-channel spectrometer 306 for recordingspectra. A photonic mixer device (abbreviated: PMD) chip is anoptoelectronic detector which registers both amplitude and phase (i.e.the time profile) of a received light pulse or of time-modulated light.By modulating the excitation energy, for example by switching theprimary particle beam off and on, or by changing the accelerationvoltage (and hence the mean energy of the primary particles), it ispossible to register and detect time-varying spectral properties of theemitted photons. Therefore, this means that the released luminescencelight can be detected in a time-resolved manner, with a time resolutionof 1 ns being possible. The time-resolving photon detector may e.g. beembodied in the form of a matrix sensor or a line sensor or a pointsensor. Alternatively, it is feasible to achieve the time resolution byvirtue of e.g. the excitation being provided in the form of a shortpulse and the resultant luminescent response being detected in atime-dependent manner. Another option lies in registering the emittedluminescence signal in a time-resolved manner with the aid of aspectrometric measurement arrangement, which comprises a fast shutter onthe entry slit.

A further advantageous embodiment comprises a first spectrometer, whichuses the radiation portion undergoing higher-order diffraction, that isto say e.g. first, second or third order, for the detection, and also asecond spectrometer, which uses the radiation portion undergoingzero-order diffraction in the first spectrometer. By using thezero-order radiation, the second spectrometer can be operated at thesame time as the first spectrometer, without the first spectrometerlosing performance in the process. This is possible because the amountof light incident on the first spectrometer is not reduced and thereforethe function of the first spectrometer is not impaired by the operationof the second spectrometer. It was found to be advantageous if the firstspectrometer e.g. registers a wavelength range from 350 nm-1700 nm,while the second spectrometer registers a narrower wavelength range,e.g. 360 nm-780 nm, and operates at a higher resolution than the firstspectrometer. However, the invention is not restricted to this exemplaryembodiment since the properties of the first and of the secondspectrometer can be selected depending on the problem posed. Thus, it isfor example also feasible for adjacent wavelength ranges to beregistered by the first and second spectrometer by virtue of the firstspectrometer registering a first wavelength range and the secondspectrometer registering a second wavelength range, wherein the firstand second wavelength range differ from one another and adjoin oneanother or do not adjoin one another.

In contrast to conventional spectrometers, in which the spectrometricmeasurement needs to be interrupted for referencing, it is moreoverpossible to reference the spectra simultaneously and in parallel. Thisis brought about by virtue of a plurality of channels being used, and soseparate channels can be used for referencing. This can be brought aboutby virtue of the light beam being split losslessly or approximatelylosslessly—for example via a dichroic mirror—such that part of the lightis fed to the spectrometric measurement while another part of the lightserves for carrying out the referencing. This can be brought about byvirtue of minimum and maximum value of the measurement arrangement beingset with the aid of an external standard, the luminescence property ofwhich is known. Alternatively, the sample itself can be employed asinternal reference standard. To this end, luminescence signals, whichare emitted by the sample but are not object of the actual analysis, areused to set the measurement arrangement for the examination and/or tocompensate for undesired system changes.

As depicted in FIG. 4, the light-entry openings 402, 403, 404, 405 ofthe optical fibers 401, 401 a, 401 b, 401 c can have differentembodiments, for example as a polished fiber end face 402, as an angledpolished fiber end face 403, as a spherical optical unit 404 or as aprism 405. In the simplest case—the polished fiber end face 402—thefiber end is embodied with a straight cut with a polish. Alternatively,the fiber end can be cut-off at an angle and polished such that anangled polished fiber end face 403 was generated. Advantageously, theangle should be selected depending on the utilized material in such away that no adverse effects, such as e.g. total internal reflection,occur. A spherical optical unit 404 is understood to mean that the fiberend is embodied as a spherical or hemispherical lens element, or elsewith an aspherical optical unit. In the case of the prism 405, the fiberend is embodied as a prism optical unit. The various embodiments 402,403, 404, 405 differ in terms of achievable numerical aperture (NA),which may typically lie between 0.22 and 0.44.

It was found to be advantageous for the various embodiments of thelight-entry openings to be combined in a detection device. Here, theembodiment of each individual light-entry opening should be selected,depending on the point on the spherical surface segment on which thislight-entry opening is situated, in such a way that the totality oflight-entry openings capture the light emitted by the sample material asefficiently as possible.

In a particularly advantageous embodiment, the light-entry openings areantiglare—independent of the respective configuration. By way ofexample, the antiglare property can be achieved by the application of amicrostructured surface or suitable coating.

An additional metalization of the surfaces of the optical fibers byvapor deposition or sputtering of e.g. aluminum or gold has theadvantageous effect that the optical fibers become electricallyconductive, and so this can prevent undesired electric charging of thecomponents during the operation of the particle-optical device.Alternatively, the electric conductivity of the optical fibers can bebrought about by coating with indium tin oxide (ITO) such that aconductive surface coating is obtained, which is moreover transparent.

A further advantageous embodiment is depicted in FIG. 5a (top view) andFIG. 5b (sectional view). In this embodiment, the various embodiments ofthe light-entry openings depicted in FIG. 4 are combined in such a waythat a planar structure is generated, via which an angle-resolveddetection is possible. Here, the light-pickup elements are arranged insuch a way that the totality of light-entry openings of the manylight-pickup elements are arranged in a plane. An advantage thereof isthat the detection device 105 can be installed in the particle-opticaldevice 101 in a space-saving manner, for example between sample 103, 502and particle-optical column 106. In the planar embodiment, an opening503 is cut-out—preferably in or near the center of the planarstructure—in which the continuation of the optical axis 104 of theparticle-optical device 101 is situated. The primary particle beam isdirected to the surface of the sample 502 through this opening 503. Viaoptical fibers 501, the photons picked up by the light-entry openingsare, as already described in the exemplary embodiment in FIG. 3, guidedto the entry slit 504 of a multi-channel spectrometer 505, which maycomprise an evaluation unit, and analyzed there.

FIG. 6 depicts a further advantageous embodiment of the invention in thesectional view. In this embodiment, the detection device 105 comprises amultiplicity of light-pickup elements 602, of which two light-pickupelements 602 are depicted in an exemplary manner. The light-pickupelements 602 are embodied as collecting optical units and connected tominiature spectrometers. The collecting optical units of the miniaturespectrometers 602 are arranged in a plane above the sample 603. By usingmirrors 604 and employing the Scheimpflug effect, it is possible viathis planar arrangement of light-pickup elements 602 and miniaturespectrometers to detect, in an angle-resolved manner, photons emittedwhen the primary particle beam 601 is incident on the sample 603. Thedetection device comprises mirrors 604, which are arranged in such a waythat photons are deflected in such a way that they are incident on acollecting optical unit and are detected. In order to employ theScheimpflug effect, the main plane of the collecting optical unit of therespective miniature spectrometer and the image plane of the miniaturespectrometer are tilted at a specific angle with respect to one anothersuch that the sample plane, main plane of the collecting optical unitand image plane of the miniature spectrometer intersect along a commonstraight line. If this condition is satisfied, the sample 603 can beimaged in focus over large regions, even if the sample plane is at anangle in relation to the image plane of the miniature spectrometer. Inthis embodiment too, it is particularly advantageous that the detectiondevice can be installed in the particle-optical device 101 in aspace-saving manner, for example between particle-optical column 106 andsample 603.

FIG. 7 depicts a further exemplary embodiment, in which the number ofelements in the beam path is minimized such that the luminescence lightcan be used particularly efficiently. The detection device 105 comprisesan imaging grating 702 and a detector 704. The imaging grating 702 canbe embodied as a concave hemispherical surface. Advantageously, thehemispherical surface has an opening 703, which can be penetrated by theprimary particle beam 701 in order then to be incident on the sample 705lying under the imaging grating 702. In an alternative embodiment, theimaging grating 702 is merely embodied as a segment 706 of thehemispherical surface. In both embodiments, the imaging grating 702 isarranged in such a way that photons released by the sample 705 aredispersed such that a spectrum is generated. The generated spectrum isdetected and stored by detector 704. The components of the detectiondevice 105 are therefore arranged and designed in such a way thatluminescence light is emitted in all spatial directions when a primaryparticle beam 701 is incident on the sample 705. Here, a first partialbeam 707 of the luminescence light is reflected at the grating 702 anddirected in the form of a second partial beam 708 in the direction ofthe detector 704 such that the second partial beam 708 is incident onthe detector surface 704. Here, partial beams 707, which were emitted indifferent solid-angle ranges by the sample 705, are incident on thedetector surface 704 at different points and are detected there. On theother hand, partial beams 707 emitted by the sample 705 are dispersed onthe grating such that they—split into the wavelengths thereof—areincident on the detector surface 704 and analyzed spectrally. This isbrought about independently of the point of incidence on the sample 705.The detector 704 can be embodied as a line detector or as a matrixdetector, wherein the use of a matrix detector enables a spatialresolution. As a result of the spatial resolution of the matrix detector704, it is therefore possible, in an angle-resolved manner, to detectand register the luminescence light emerging from the sample 705 sinceluminescence light emitted into different solid-angle ranges isdeflected to different points of the matrix detector 704 by the grating702.

It is a characteristic of this exemplary embodiment that the number ofelements in the beam path has been minimized since the light-emittingpoint on the sample 705 simultaneously constitutes the entry slit of aspectrometric measurement arrangement. The spectrometric measurementarrangement comprises the sample (as entry slit) 705, the imaginggrating 702 and the detector 704. In this manner, the luminescence lightcan be employed with the greatest possible efficiency.

As an alternative to the above-described particularly advantageousspherical embodiment, the imaging grating 702 can have an asphericalembodiment. It was moreover found to be advantageous if the imaginggrating 702 was produced holographically, independently of the form ofthe embodiment.

FIG. 8 shows the flow chart of a method according to the invention forspectroscopic analysis of samples. A primary particle beam directed tothe sample is generated in a first step 801. The primary particle beamcan be an electron beam and/or an ion beam. The primary particle beam isincident on the sample and releases photons from the sample due to theinteraction between primary particle beam and sample material. Thereleased photons can move along a multiplicity of possible trajectories,wherein each one of the possible trajectories n is characterized by anelevation angle h_(n) and an azimuth angle a_(n), and equal or similartrajectories are combined to form solid-angle ranges of thetrajectories. In the next step 802, the released photons are capturedsimultaneously by a multiplicity of light-pickup elements, wherein eachindividual light-pickup element registers a solid-angle range of thetrajectories. In the next step 803, the captured photons are forwardedto an analysis system. The analysis system comprises a multiplicity ofevaluation units, and so an evaluation unit is assigned to eachlight-pickup element. The analysis system can comprise a multi-channelspectrometer, i.e. a spectrometer with which a plurality of completespectra can be recorded simultaneously, or a multiplicity ofminiaturized spectrometers. In step 804, optical spectra are recorded insuch a way that a spectrum is generated for each light-pickup element onthe basis of the photons captured by this light-pickup element.Therefore, this means that each recorded spectrum corresponds to asolid-angle range of the trajectories. Thus, cathodoluminescence isdetected separately over a multiplicity of different solid-angle ranges,wherein a multiplicity can advantageously be ten or more solid-angleranges. In a subsequent optional step 805, the recorded optical spectraare evaluated. This is preferably brought about in a computer-assistedmanner since large amounts of data have to be processed. It isadvantageous if comparison spectra are already available and stored in adatabase, to which comparison spectra the newly obtained spectra can becompared. It is moreover feasible for this data collection to becomplemented and extended by the newly obtained and evaluated spectrasuch that the device used for the method can be calibrated by the userfor a specific application.

Since the spectra can be obtained in an angle-resolved and/ortime-resolved and/or spatially resolved manner, it is sensible toevaluate the spectra using chemometric processes suitable formultidimensional data. Here, the angular resolution provides informationabout material properties and texture of the sample, also from differentsample depths. The time resolution supplies information about thekinetics of the luminescence reaction, which in turn allows conclusionsto be drawn about the material properties of the sample material. Sincethe emission of luminescence light is influenced by the surfacetopography of the sample, it is possible to draw conclusions about thesample topography.

The processes applied during the evaluation are dependent on therespective sample and the respective question. The multidimensionalityof the data requires a computer-assisted evaluation, with differentprocesses being known, e.g. those described in Naes T. et al. (2002): “AUser-Friendly Guide to Multivariate Calibration and Classification”, NIRPublications, Chichester, UK and in Marini, F. et al.: “ArtificialNeural Networks in Chemometrics: History, Examples and Perspectives,Multivariate Analysis and Chemometrics applied to Environmental andCultural Heritage”, Nemi (RM), 2-4 Oct. 2006, Italy, such as, forexample, multivariate statistical methods, discriminant and clusteranalysis, multiple linear regression, principal component regression,principal component analysis, multivariate curve analysis, wavelettransform, genetic algorithms, neural networks or support vectormachines. Here, the evaluation is carried out in such a way that theobtained results can be represented in a user-friendly manner.

All embodiments described previously are not restricted to the detectionof photons generated by cathodoluminescence. It is also possible todetect light emitted as a result of other excitation processes, e.g. asa result of photoluminescence, electroluminescence, chemoluminescence orbioluminescence. Moreover, it is feasible to trigger luminescencephenomena with the aid of a focused ion beam and to detect these inaccordance with the invention. By way of example, such a focused ionbeam can be generated via a gallium ion source, wherein the emittedgallium ions are accelerated and focused with the aid of suitablelens-element systems such that they are incident on the sample surfaceas a focused ion beam. Alternatively, use can also be made of other ionsources, for example a helium gas field ion source.

LIST OF REFERENCE SIGNS

-   101 Particle-optical device-   102 Sample chamber-   103 Sample-   104 Optical axis-   105 Detection device-   106 Particle-optical column-   107 Analysis system-   108 Detector-   109 Particle beam source-   110 Lens-element system-   111 Lens-element system-   112 Aperture stop-   113 Deflection system-   201 Primary particle beam-   202 Light-pickup element with collecting optical unit-   203 Sample-   204 Solid-angle range of a trajectory-   205 Miniature spectrometer-   206 Trajectory-   207 Analysis system-   208 Wall of the sample chamber-   209 Sample chamber-   210 Intermediate surface-   301 Primary particle beam-   302 Light-pickup element with light-entry opening-   303 Sample-   304 Solid-angle range of a trajectory-   305 Entry slit-   306 Multi-channel spectrometer-   307 Optical fiber-   308 Trajectory-   401 Optical fiber-   401 a Optical fiber-   401 b Optical fiber-   401 c Optical fiber-   402 Fiber end face-   403 Angled fiber end face-   404 Fiber end with a spherical optical unit-   405 Fiber end with a prism-   NA Numerical aperture-   501 Optical fiber-   502 Sample-   503 Opening-   504 Entry slit-   505 Multi-channel spectrometer-   506 Trajectory-   601 Primary particle beam-   602 Miniature spectrometer-   603 Sample-   604 Mirror-   701 Primary particle beam-   702 Imaging grating-   703 Opening-   704 Detector-   705 Sample-   706 Hemispherical segment-   707 First partial beam-   708 Second partial beam-   801 Step: generating a primary particle beam-   802 Step: capturing photons-   803 Step: forwarding photons-   804 Step: recording spectra-   805 Step: evaluating spectra

The invention claimed is:
 1. A device, comprising: a particle beamsource configured to generate a primary particle beam directable to asurface of a sample so that, when the primary particle beam is incidenton the sample, photons are released from the sample due to theinteraction between primary particle beam and the sample; light-pickupelements configured to capture photons released from the sample, eachlight-pickup element being configured to capture photons emitted in asolid-angle range; conduction elements configured to forward capturedphotons to an evaluation unit; and an analysis system comprising aplurality of evaluation units so that photons captured by eachlight-pickup element are spectrally analyzable, wherein the light-pickupelements are arranged on a segment of a spherical surface, and thesegment of the spherical surface has a radius extending perpendicular tothe surface of the sample.
 2. The device of claim 1, wherein thelight-pickup elements are arranged in a plane.
 3. The device of claim 1,wherein the evaluation units of the analysis system compriseminiaturized spectrometers, and the light-pickup elements comprisecollecting optical units.
 4. The device of claim 1, wherein the analysissystem comprises a multi-channel spectrometer.
 5. The device of claim 4,wherein the multi-channel spectrometer comprises a time-resolving photondetector.
 6. The device of claim 1, wherein the light-pickup elementscomprise light-entry openings of optical fibers.
 7. The device of claim6, wherein a light-entry opening comprises a member selected from thegroup consisting of a polished fiber end face, an angled polished fiberend face, a spherical optical unit, and a prism.
 8. The device of claim6, wherein the light-entry openings comprise antiglare.
 9. The device ofclaim 6, wherein optical fibers comprise metallized surfaces.
 10. Thedevice of claim 1, wherein the particle beam source comprises anelectron source.
 11. The device of claim 1, wherein the particle beamsource comprises an ion source.
 12. The device of claim 1, wherein theanalysis system comprises a first spectrometer and a secondspectrometer, the second spectrometer being configured to use aradiation portion diffracted in the zero order in the firstspectrometer.
 13. The device of claim 1, wherein, between the particlebeam source and the sample, the particle beam path does not pass throughthe light-pickup elements.
 14. A method, comprising: directing a primaryparticle beam to a surface of a sample so that the primary particle beamis incident on the sample and photons are released from the sample dueto the interaction between the primary particle beam and the sample andso that released photons move along a multiplicity of possibletrajectories; simultaneously capturing the released photons via amultiplicity of light-pickup elements, wherein each individuallight-pickup element corresponds to a solid-angle range of thetrajectories; forwarding the captured photons to an analysis system,wherein the analysis system comprises a multiplicity of evaluation unitsso that an evaluation unit is assigned to each light-pickup element; andrecording optical spectra so that a spectrum is generated for eachlight-pickup element on the basis of the photons captured by thislight-pickup element, wherein the light-pickup elements are arranged ona segment of a spherical surface, and the segment of the sphericalsurface has a radius extending perpendicular to the surface of thesample.
 15. The method of claim 14, further comprising evaluating therecorded optical spectra.
 16. The method of claim 14, wherein theprimary particle beam comprises an electron beam.
 17. The method ofclaim 14, wherein the primary particle beam comprises an ion beam. 18.The method of claim 14, further comprising evaluating the obtainedspectra via chemometric processes.
 19. The method of claim 14, whereinthe light-pickup elements are arranged in a plane.
 20. The method ofclaim 14, wherein the evaluation units of the analysis system compriseminiaturized spectrometers, and the light-pickup elements comprisecollecting optical units.
 21. The method of claim 14, wherein theparticle beam is produced by a primary particle beam source, and whereinbetween the particle beam source and the sample, the particle beam pathdoes not pass through the light-pickup elements.
 22. A device,comprising: a particle beam source configured to generate a primaryparticle beam directable to a sample so that, when the primary particlebeam is incident on the sample, photons are released from the sample dueto the interaction between primary particle beam and the sample;light-pickup elements configured to capture photons released from thesample, each light-pickup element being configured to capture photonsemitted in a solid-angle range; conduction elements configured toforward captured photons to an evaluation unit; and an analysis systemcomprising a plurality of evaluation units so that photons captured byeach light-pickup element are spectrally analyzable, wherein, betweenthe particle beam source and the sample: the particle beam path does notpass through the light-pickup elements; and the particle beam pathpasses between at least two of the light-pickup elements.